Phosphonate lubricants



Unite PHOSPHONATE LUBRICANTS No Drawing. Filed May 9, 1957, Ser. No. 658,034 4 Claims. (Cl. 252-49.8)

This invention relates to new and useful improvements in high-temperature synthetic lubricants and more particularly to a novel class of esters of phosphonic acids which are particularly useful as high-temperature lubricants.

In recent years there has arisen a need for thermally stable lubricants capable of withstanding the severe conditions encountered in high-temperature engines such as are used in jetand rocket-propelled aircraft and missiles and in automotive gas turbines. A considerable amount of research has been done on synthetic lubricants, such as esters, silicones, polyalkylene glycols, perfluorocarbons, halogenated hydrocarbons, silicate esters, and phosphate esters. These recent developments are reviewed in a number of publications among which are Review of Synthetic Lubricants, D. H. Moreton, Lubrication Engineering, April 1954, pages 65 to 73, and Synthetic Oils Start Moving, Chemical and Engineering News, Sept. 3, 1956, pages 4244 to 4248. Among the numerous compounds tested for use as lubricants for high-temperature operation, the phosphorus-containing esters have been very promising due to their high lubricity, low volatility, and low flammability. The phosphorus compounds which have received the most attention have been aliphatic, aryl and mixed esters of phosphoric acid, esters of alkyl and aryl phosphonic acids, and aliphaticand aryl-substituted phosphine oxides. The properties sought in phosphorus-containing synthetic lubricants are:

(1) High viscosity index (V.I.).

(2) Low volatility.

(3) Low flammability.

(4) High thermal stability.

(5) High lubricity.

Phosphate and phosphonate esters in general have superior properties of lubricity, non-inflammability, and low volatility. These esters, however, are variable in thermal stability and viscosity index. For example, triaryl phosphates have high thermal stability but low V.I. Trialkyl phosphates, on the other hand, have low thermal stability but high V.I. Mixed alkyl aryl phosphates have low thermal stability and high V.I. It appears that the POR linkage in alkyl phosphates tends to decompose at high temperature to produce an acid and an olefinic hydrocarbon. Aryl phosphonates have high thermal stability and low viscosity index while alkyl phosphonates have high viscosity index and low thermal stability. Mixed aryl esters of alkane phosphonic acids having short carbon chains in the acid similarly have high thermal stability but very low viscosity index.

It is, therefore, an object of this invention to provide 1: tes Patent 9 a new and improved synthetic lubricant which combines the properties of high lubricity, high thermal stability, low flammability, low volatility, and high V.I.

Another object of this invention is to provide a new and improved phosphorus-containing synthetic lubricant which combines high thermal stability and high V.I.

A feature of this invention is the provision of a novel phosphonate ester which is useful as a high-temperature synthetic lubricant, combining properties of high lubricity, high thermal stability, low flammabilty, low volatility and high V.I.

Another feature of this invention is the provision of a new class of phosphonate esters, consisting of diaryl esters of alkane phosphonic acids having ether linkages in the alkyl radical attached to the acid group, which are especially useful as high temperature lubricants.

Other objects and features of this invention will become apparent from time to time throughout the specification and claims as hereinafter related.

This invention is based upon our discovery that certain esters of ether-substituted alkane phosphonic acids are especially stable at high temperatures and provide a combination of desirable lubricating properties including high viscosity index. In particular, this invention is based upon our discovery that diaryl esters of ethersubstituted alkane phosphonic acids, in which the alkyl carbon chain contains one or more ether linkages, combine properties of high thermal stability and high V.I. with other desirable properties for high-temperature lubrication, such as low volatility, low flammability and high lubricity. These phosphonate esters have the general formula (ArO) RPO, Where R is an alkyl group having one or more ether linkages in the carbon chain (e.g. where R is 2-butoxyethyl, or 2-(2-n-butoxyethoxy) ethyl), and Ar is an aryl group including phenyl and naphthyl, and halogenated, aryl and alkyl derivatives thereof. In general, phosphonate esters combining any aryl and substituted alkyl groups as above defined, which are liquid at room temperature, and through the range of operating temperatures for the surface to be lubricated, are useful as lubricants. Phosphonate esters which are useful as lubricants include: diphenyl Z-butoxyethyl phosphonate, bis (chlorophenyl) 2-butoxyethyl phosphonate, bis (diphenyl) 2-(2-n-butoxyethoxy) ethyl phosphonate, dinaphthyl Z-(Z-n-butoxybutoxy) propyl phosphonate, dio-tolyl 4-propoxybutyl phosphonate, bis (propylphenyl) 4-(3-n-butoxypropoxy) butylphosphonate.

In a series of experiments of number of phosphoruscontaining compounds, including triaryl phosphates, mixed aryl alkyl phosphates, phosphonate esters, and trialkyl phosphine oxides, were prepared and compared for the physical properties required of a high-temperature lubricant.

EXAMPLE I The phosphonate esters of this invention are preferably prepared using the Michaelis-Arbuzov reaction as described by Kosolapofl, Organo-Phosphorus Compounds," Wiley & Sons (1950), at page 121 thereof. In one experiment, di-m-tolyl-2-n-butoxyethyl phosphonate was prepared as follows: 171.8 g. (0.488 mol) of tri-mtolyl phosphite was charged to a 500 ml. round-bottom flask fitted with a stirrer, reflux condenser and heating mantle. To this, 88.3 g. (0.488 mol) of Z-n-butoxyethyl m-tolyl Z-n-butoxyethyl phosphonate.

Several diaryl alkane phosphonates were prepared by the same general method and compared for physical properties as shown in .the following table:

Table '1 PROPERTIES OF DIARYL ALKANE PHOSPHONATES (ArO):RPO

The compounds in the above table are:

A-di-o-tolyl n-amylphosphonate B-dl-o-chlorophenyl n-arrylphnsphonate Gdi o-tolyl 2-ethylhcxylph sphonate D-di-rn-tolyl 2-bub0xyothylph0sphonate E-di-m-tolyl Z-(Z-n-butoxycthoxy) ethylphosphonatc The structures of compounds D and E above are as follows:

g CH3 CH: i

'Fromthese and other experiments we have found that 'the lubricant properties of diaryl alkane phosphonates improve as ether linkages are introduced into the alkyl :group. With increasing length of the carbon chain and increase in the number of ether linkages in the alkyl group, the pour point is lowered and the viscosity index is increased. In comparative data with other phosphorus compounds, which will be shown hereinafter, it was established that the diaryl alkane phosphonates which have ether linkages in the alkyl radical have the superior properties of thermal stability and viscosity index which are required for it to function satisfactorily as a high-ternperature lubricant.

EXAMPLE H Several procedures are available for the preparation of triaryl phosphates which were used for comparison with the lubricant liquids which form this invention. In one method a mixture of phosphorus oxychloride and an excess of the appropriate phenol were heated to about 200 C. for at least one hour with anhydrous magnesium chloride present as a catalyst. Hydrochloric acid was liberated in the reaction and escaped from the reflux condenser. After the mixture had cooled, pyridine was added to combine with any remaining hydrochloric acid. The solid pyridine hydrochloride was removed either by filtration or by water-washing. The product was then washed free of any remaining pyridine, dried and distilled. This procedure is described by C. F. Raley, Jr., in WADC Technical Report 53-337, page 36, November 1953, and by Kosolapoff in Organo Phosphorus Compounds, page 229 (1950).

In another method for preparing symmetrical triaryl phosphates, three equivalents of pyridine and threeequivalents of the appropriate phenol were dissolved in ether. This was held at about 5 to 10 C. and an ether-solution of one equivalent of phosphorus oxychloride was added slowly. When the addition was complete, the ether solution was refluxed for about two hours. The mixture was then cooled and the pyridine hydrochloride was removed by filtration. The product was washed with .waterto remove excess pyridine, stripped free of ether and water, and distilled. Unsymmetrical triaryl phosphates can be prepared by modifying the above procedures slightly. For example, in the synthesis of di-m-tolyl o-diphenyl phosphate the first step was to prepare di-rn-tolylphosphoryl chloride by the reaction of one equivalent of phosphorus oxychloride with two equivalents of m-cresol. The product was then distilled and reacted with one equivalent of .o-phenyl phenol. A number of triaryl phosphates were prepared by the above procedures and physicahproperties determined as set forth in Table II.

Table II PROPERTIES OF TRIARYL PHOSPHATES (ArO)aPO Molec lar Wt. percent, P Viscosity S.U.S. at-

Weight Pour Triaryl Phosphate V.I. P I-in;

Calc'd Found Calcd Found F. 130F. 210 F.

.trl-p-{plgyl (obtained commer- 368.4 8.41 190.4 87.0 40.9 91 5 c a y tri-o-rhlorophenyl 410 7. 21 7. 4 315 45. 9 3 +5 his (3, 5-dimethylpheny1) 395 7.55 7.6 424.0 151.2 47.'l 86 +5 dl-m-tolyl o-diphenyl. 430.4 410 7.20 7.3 773 237.3 54.2 85 +15 dim-toltl o-nitrophenyl 399.3 400 7.76 7.2 323.7 130.9 46.8 7 5 di-rn-tolyl 2, 4-di2l10lor0phenyl" 423. 2 410 7. 32 7. 4 222. 2 95. 3 41. 6 0 dl-m-tolyl p-(l, 1, 3, B-tetra- 466.5 400 6. 64 4.3 1231 371.2 65.2 .53 +10 ruethylbutyl) phenyl.

EXAMPLE In The alkyl aryl phosphates prepared for comparison with the synthetic lubricants of this invention were prepared by the process of Gamrath, Hatton and Weesner, as reported in Ind. Eng. Chem, 46, 208 (1954). As an example of this method, the synthesis of n-hexyl di-mtolyl phosphate will be described in detail. First, n-hexyl phosphoryl dichloride was prepared. A suitable flask was charged with one mol of phosphorus oxychloride and cooled to about 5 to C. With continued cooling and stirring, one mol of l-hexanol was added dropwise. After the alcohol had been added, the hydrogen chloride formed in the reaction was removed as a gas by allowing the reaction mixture to warm to about 25 C. and reducing the pressure over the reaction mixture. The re maining material, which was essentially pure n-hexyl phosphoryl dichloride, was then added to an aqueous solution of 2 mols of sodium m-cresylate, while the temperature was maintained below 25 C. When the reaction was complete, stirring was discontinued and the two layers were separated. The ester layer was purified by washing with dilute sodium hydroxide solution and water, followed by stripping at 100 C. using a nitrogen purge and water-aspirator vacuum. This procedure produced a product which was sufficiently pure so that further purification was not needed. A number of alkyl aryl phosphates were prepared by the above procedure and physical properties determined as set forth in Table III.

Calc'd Found Molecular Weight 386. 6 410 Weight Percent, P 8.01 7.8

Viscosity S.U.S. at-

The phosphorus-containing liquids produced in Examples I to IV were found to be of high lubricity, low volatility, and low flammability. These liquids were tested for thermal stability and viscosity index (V.I.) to determine their suitability for use at elevated temperatures. In testing these liquids for thermal stability, about 20 ml. of the liquid under test is weighed into a ml. graduated Pyrex test tube having an CD. of 25 mm., and equipped with a female 24/40 joint at the top and a hook so that it can be hung for weighing. A .Pyrex unit fits in the joint at the top of the test tube and has a side tube of Table III PROPERTIES OF ALKYL DIARYL PHOSPHATES (R0) (Ar0)2PO Molecular Wt. percent,P. Viscosity SUS at-- Weight Pour Alkyl Diaryl Phosphate V.I. 15 012 1;

Calcd Found ones Found 100F. 130F. 210F.

n-propyl di-m-tolyl 320.3 300 9.67 7.1 58.9 4.5.6 34.2 44 70 n-amyl di-m-tolyl 348.4 330 8. 89 8.3 62.8 47.5 34.8 50 70 dodecyl dl-m-toly1 446.6 410 6. 94 6.9 86.9 38.5 113 20 cyclohexyl diphenyl 332.3 300 9.32 8.7 99.7 61.9 38.0 24 cyclohexyl dio-chlorophenylufi 365.8 370 8.47 7.2 279.3 118.5 45.4 -3 -15 4-methylcyclohexyl di-m-tolyl 374.4 310 8.27 7.3 96.4 60.2 37.4 2 -45 EXAMPLE IV about 7 mm. O.D. extending through the side and about Tertiary phosphine oxides (R PO) used for comparison with the synthetic lubricants of this invention are prepared from an alkyl halide and phosphorus oxychloride by the Grignard reaction. In preparing tris (Z-ethylhexyl) phosphine oxide, the standard procedure was used to prepare Z-ethylhexyl magnesium bromide from the alkyl bromide and magnesium. Then 1 mol of phosphorus oxychloride in ether was added slowly to an ether solution of three mols of the Grignard reagent. The reaction was very exothermic and cooling with ice water was necessary to maintain the solution under mild reflux conditions. To obtain good yields by this process it is essential that the Grignard reagent be always in excess. The reaction product was then decomposed to yield tris (Z-ethylhexyl) phosphine oxide by the slow addition of a saturated aqueous solution of ammonium chloride. in this decomposition step a considerable amount of heat was evolved and cooling with an ice-water bath was necessary. The ether layer was removed and washed successively with water, dilute sodium hydroxide solution and water. Final purification of product was obtained by nitrogen-stripping 2 inches out of the bottom for passing nitrogen through the test tube. An air condenser of about 21 mm. OD. and 50 cm. long is inserted at the top and. prevents a loss of all but the most volatile breakdown products, thus permitting the use of the apparatus in the open without danger of toxic vapors in the room. The test tube charged with liquid to be tested is placed in an electrically heated furnace and heated to the desired testing temperature. The standard high-temperature test used for these synthetic lubricants is for five hours at 550 F. A more severe test is also used in which the liquids are heated to 700 F. for three hours. Following the prescribed period of heating, the sample holder is removed and allowed to cool under nitrogen atmosphere and the liquid is measured for change in physical properties. In particular, the liquids tested are measured for change in molecular weight, viscosity, V.I., pour point, acid number, and for loss in weight. Of these various properties, the change in acid number is the most significant measure of thermal instability since it indicates the breakdown of the ma terial into acid products. The change in properties of the phosphorus-containing liquids produced in Examples I to jectedto the It is thus seen that the etherhonates have unexpectedly and Table IV compounds were further tested by being sub more severe thermal stability test for three hours at 700 F. and were not appreciably affected by exposure to such an elevated temperature.

These 5 substituted alkane phosp THERMAL STABILITIES OF TRIARYL PHOSPHATES A'I 550 F.

4 17 26 3 7 1 m m 4 s0 52 mos mm .0 m .0 m on De mm M am men. 4 21 55 .l. V. 26 6 77 8 YH 44. 21 14. 12 1 V. .l O9 1 a 66 3 V 16 9 1 37 1 .bXLl 1 54 4.4 5 m mm. 11 mmm 1 1 F (mhm 11 A w hm e k m h mw. w m um m 6 5 an. m T 59 055 t yr 00 28 36 4.5 36 504 A l s 05 42 64 3 1.1 06 39 27 52 F hfl. mm N6 9% 58 .WIWW JM Mm 2 2 owL 5 5 21 w wm y M 08 WW 4 88 1 n 0 4 7 46 +2 S mm a 67 33 n .0 nu 5 T W MCG 1 24 1 E 200 0 mm H n a d m D mw mmm I v e m.m T Wm X d b u mu n A O 0 l 0 3 6 70 509 0 n s Wm 0m .3 m 0 mm on E my mm .3 .0 11 430 E w 37 2 91 4 1 0 .MKhM 3 3. W 5% 00 52 24 62 54 005 T e 4 9 I 0 2 N top 1 3 l0 1 1 .t 2 yr 0 0 2 2 7 1 2 n A h I ulo m fl. 0 23 44. H n fm H h thn 22 0 y P 1. m e P C S 0 0 m 0 1 5 m H W.. w% MW N MM %%M H W oe 1 0 M 5 WW .m 2 P w 4a 0 mm mm 1 2 P m mm as 3 Wm aw :4 t d D O 00 5 91 31 557 0 1 aw & .06 v @m N mmm. mm. M 44 0 R d A d h I V M .l 00 23 81 87 05 51 V m W 0 5O 58 79 92 556 O .IV. 31 .9 .2 50 72 9 14. 6 12 e D a 37 1 21 45 1 1 T O 3 .04 88 U H L m 6 3 2 k A m m 23 BB 33 0 ce 5a a Y am b N ha n 43 93 12 557 T DL. 8 O .w n K 1 98 2 d T d D.

m m 44 0 A P a v mm m w 23 um mm s m a .3 20 mm mmm .1 O t 08 5 39 B 01 O1 33 0 n w. 1 1 H WM 11 s 3 P mm .1

. m mu F d D.

n u N n u T o n n n n u M n S n u n n I E B I e T e A t I O A h e... c 3.5.. a

m .W nn nn unmnR M m m g u mun nm t M M." n mnu muum Hut 0 m zmzwzi s H m is a M M m s w m v m r E. eu an an aums "m T m mm s ms um m R {a m j m m u arrmrr Tr Tr. rrirr If r r. r I r I nmm mmmmmmmmmmmmmm m mmmmmmwmwmmmw t m mmmmmmwmmwmmwmmmmmt m 8 S 5 .1 f ei. 6.1 8 1 59 n 9 efflef me $0 1 efn BM BA BA BA BA BAm BA BA BAmBMm T BM BAwBAwBMwBA BAw O E E 0 0 0 o .B (c... .E H 0 d h. B B O M M. A v v v v. P M A v v v P M A v v v P P IV,'folloWing their subjection to the 550 F. stability test is set forth in Tables IV, V and VI as follows As a result of these tests, it was found that those phoshorus compounds which combined most favorably high thermal stability and high V.I. were the diaryl alkane phosphonates having one or more ether linkages in the 'alkyl group connected .to the phosphorus atom.

where Ar is selected from the group consisting of lower alkyl substituted phenyl and naphthyl radicals, and R is a polyether radical containing at least two ether linkages. 2. Di-m-tolyl 2-(2-n-butoxyethoxy) ethyl phosphonate. 3. A method of reducing friction between two relatively movable surfaces which consists of incorporating between said surfaces an amount, sufiicient to lubricate said surfaces, of a liquid phosphonate as defined in claim 1.

4. A method for reducing friction between two rela- 10 tively movable surfaces which consists of incorporating between said surfaces an amount of di-m-tolyl 2-(2-nbutoxyethoxy) ethyl phosphonate sufficient to lubricate said surfaces.

References Cited in the file of this patent UNITED STATES PATENTS 2,500,022 Brown Mar. 7, 1950 2,652,416 Coover et a1 Sept. 15, 1953 2,706,534 Hunter Apr. 19, 1955 2,712,363 Vaughn et a1 u July 5, 1955 FOREIGN PATENTS 701,838 Great Britain Jan. 6, 1954 509,034 Canada Jan. 11, 1955 

1. DIARYL ALKANE PHOSPHONATES OF THE FORMULA
 3. A METHOD OF REDUCING FRICTION BETWEEN TWO RELATIVELY MOVABLE SURFACES WHICH CONSISTS OF INCORPORATING BETWEEN SAID SURFACES AN AMOUNT, SUFFICIENT TO LUBRICATE SAID SURFACES, OF A LIQUID PHOSPHONATE AS DEFINED IS CLAIM
 1. 